Iran this week punctuated ten days of naval exercises in the Strait of Hormuz and threats to close it
with a warning to U.S. Navy ships to stay out of Persian Gulf,
which requires passage through the strait. The tough talk may have temporarily juiced oil prices, but it failed to impress
militarily. Recentnewsreports have cited U.S. military officials, defense
analysts and even an anonymous Iranian official arguing that Iran likely lacks the will and
ability to block shipping in the strait. That argumentisn'tnew: Iran's economy depends on shipments through the
strait, and the U.S. Navy can keep it open, if need be. What's more, the
Iranians might be deterred by the fear that a skirmish over the strait would
give U.S. or Israeli leaders an excuse to attack their nuclear facilities.

The obviousness of Iran's bluster suggests its weakness. Empty threats generally show desperation, not
security. And Iran's weakness is not confined to water. Though Iran is more
populous and wealthier than most of its neighbors, its military isn't equipped for conquest. Like other militaries
in its region, Iran's suffers from coup-proofing, the practice of designing a military more to
prevent coups than to fight rival states. Economic problems and limited
weapons-import options have also undermined it ability to modernize its
military, while its rivalsbuy American
arms. Here's how Eugene Gholz and Daryl Press summarize Iran's conventional military capability:

Iran...lacks the equipment and training for major offensive
ground operations. Its land forces, comprising two separate armies (the Artesh
and the Islamic Revolutionary Guard Corps), are structured to prevent coups and
to wage irregular warfare, not to conquer neighbors. Tehran's air force is
antiquated, and its navy is suited for harassment missions, not large
amphibious operations across the Gulf. Furthermore, a successful invasion is
not enough to monopolize a neighbor's oil resources; a protracted occupation
would be required. But the idea of a sustainable and protracted Persian Shi'a
occupation of any Gulf Arab society--even a Shi'a-majority one like Bahrain--is
far-fetched.

Despite Iran's weakness, most U.S. political rhetoric--and
more importantly, most U.S. policy--treats it as a potential regional hegemon
that imperils U.S. interests. Pundits eager to bash the president for belatedly allowing U.S. troops to
leave Iraq say it will facilitate Iran's regional dominance. The secretary of
defense, who says the war in Iraq was worth fighting, wants to station 40,000 troops in the region to keep Iran from meddling there. Even opponents of bombing
Iran to prevent it from building nuclear weapons regularly opine on how to "contain" it, as if that required great effort.

Some will object to this characterization of Iran's
capabilities, claiming that asymmetric threats--missiles, the ability to harass shipping
and nasty friends on retainer in nearby states--let it punch above its military
weight. But from the American perspective--a far-off power with a few discrete
interests in the region--these are complications, not major problems. Our
self-induced ignorance about Iran's limited military capabilities obscures the
fact that we can defend those interests against even a nuclear Iran at far
lower cost than we now expend. We could do so from the sea.

The United States has two basic interests in the region. The
first is to prevent oil-price spikes large enough to cause economic trouble.
Although it's notclear that an oil-price shock would greatly damage the U.S.
economy, we don't want to chance it. That is why it makes sense to tell Iran
that we will forcibly keep the strait open.

Iranian nuclear weapons would merely complicate our efforts
to do so. For safety, both naval ships clearing mines there and tankers would
want Iranian shores cleared of anti-ship cruise missiles and their radars,
although doing so is probably not necessary to keep strait cargo moving. The possibility of
nuclear escalation makes attacking those shore-based targets tougher. But the
risk of escalation is mostly Iran's. By attacking U.S. ships, they would risk
annihilation or a disarming first strike. Given that, it is hard to see how
nuclear weapons make closing the strait easier.

The second U.S. goal in the region is to prevent any state
from gathering enough oil wealth to extort us or build a military big enough to
menace us. That means conquest. The vastness of our military advantage over any
combination of Middle Eastern states makes that fairly easy to prevent. The
difficulty of credibly threatening to stop exporting the chief source of your
wealth makes the problem even smaller. Indeed, the odds of Iran becoming an oil
super-state by conquest are so low that we probably do not need to guarantee
any nearby state's security to prevent it. For example, if Iran swallowed and magically pacified Iraq, the resulting state, while a bad
thing, would create little obvious danger for American safety or commerce.
Still, if we did defend Iraq's borders, carrier-based airpower along with Iraqi
ground forces would probably suffice to stop Iranian columns at the border. The
same goes for Kuwait and Saudi Arabia.

Because threats of nuclear attack better serve defensive
goals, an Iran armed with nukes would not meaningfully change this calculus.
Iran's neighbors would not surrender their land just because Iran has nuclear
weapons, if history is any guide. And U.S. guarantees of retaliatory strikes
could back them up, if necessary. Nukes might embolden Iran to take chances
that a state worried about invasion would not. But the difficulty of subduing a
nationalistic country of 75 million already deters our invasion.

The current contretemps with Iran is no reason for
"maintaining our military presence and capabilities in the broader Middle
East," as the secretary of defense would have it. Removing U.S. forces from Iran's flanks
might strengthen the hand of the Iranian minority opposed to building nuclear
weapons, though it is doubtful that alone would be enough to let them win the
debate anytime soon. But even if Iran does build nuclear weapons, we can defend
our limited interests in the region from off-shore.